Last year saw "part-time" yakuza outnumber their full-time mob counterparts for the first time ever, the National Police Agency, which has been keeping such statistics since 1958, said Thursday.
As of the end of December, the gangster population was estimated at 84,700, down about 1,600 from a year earlier.
Full-time yakuza numbered 41,500, while part-timers or semiregular members -- those not directly affiliated with the mob -- increased slightly to 43,200. In 1991, there were an estimated 63,800 full-time mobsters, and some 27,200 part-timers.
In reality, yakuza are appearing to detach themselves from full-time mob activity by engaging in business, political or social activities in a bid to camouflage their underworld affiliation, the NPA said.
"It is an urgent task to investigate the scope of the semiregular membership and to take action against companies providing funds to crime syndicates," an NPA official said.
According to the NPA, semiregular yakuza help fund their underworld bases, and use the mob's clout to often engage in illegal activities.
The three top syndicates, Yamaguchi-gumi, Sumiyoshi-kai and Inagawa-kai, together had around 61,600 members, or 73 percent of the nation's underworld ranks, the NPA said.
The dominance of the three mobs is well established, with Yamaguchi-gumi accounting for 47 percent of the total, the NPA said.
2006 was also the first year in which gangland turf wars were not reported.
Since Monday, however, there has been a spate of mob-linked shootings in Tokyo, one fatal, apparently due to a clash between Yamaguchi-gumi and Sumiyoshi-kai.
"Gang rivalry seems to be intensifying with the advancement into Tokyo by (Kobe-based) Yamaguchi-gumi. A gangland war can break out at any time," an NPA official said.
Yamaguchi-gumi has more than 21,000 members. Tokyo-based Sumiyoshi-kai ranks second with more than 8,000 members, followed by Inagawa-kai, also based in Tokyo, with more than 5,000.